SRX250
A small case of single mindedness

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Small capacity single cylinder four stroke road bikes have been around for years, but these days have now fallen from favour as road bikes. On the used bike market, small singles are a little more common. Perhaps the two most successful small singles in recent times have been the Honda CB250RS and the Yamaha SRX250. The Honda dates from the early 1980's, whilst the Yamaha is a little newer, coming to Australia from 1984 to 1986. The little Yam has a bit of character and a good reputation. In 1998 when I got back into bikes after a bit of a break, it seemed like a good choice. I intended to keep it only for a few months, but 5 years later I can't bring myself to get rid of it - it really is a heap of fun to ride.

History

The SRX250 was released onto the world market in 1984. At the time its natural competitors were the Kawasaki BR250, the Honda CBX250 and the Suzuki GN250.

Yamaha took the just released twin cam four valve motor from its successful XT250 dirt bike series and dropped it into a twin down tube road bike frame. The engine was slightly tweaked from its XT cousins to boost power at higher engine speeds. A counter balancer shaft helped to tame most of the vibrations inherent in single cylinder designs. As was fashionable at the time, a 16 inch front wheel was fitted. A relatively strong front disc brake, good instrumentation, electric starter, half fairing and "monocross" rear suspension completed the package. It was always a relatively inexpensive model, selling generally to new motorcycle entrants, and commuters. The build quality was for its era, very high.

It's specifications remained unchanged during the three years it was sold in outside Japan. After its departure from the world market, the engine continued to power new XT250s for many years. Indeed the motor in the current TT350 and XT350 is closely related to the SRX engine.

On the road

Over the years many riders have been introduced to the pleasures of biking on SRX250s. The light weight ( 136 kg wet) and low seat height ( 750 mm.) make the bike easy to handle. The controls are light and easy to operate.

The motor delivers its modest power in a very progressive manner, with useable power coming in at a low 2500 rpm. By 5000rpm things are starting to move along nicely, with a further lift in power around 6500rpm. You can keep in front of the cars around town without ever exceeding 5000 rpm. The bike has excellent lugging power for a 250, perhaps a result of a decent flywheel effect. Cruising at 100kph sees the bike pulling about 6000 rpm in sixth gear.

Comfort for the rider is reasonable, provided a sheepskin is fitted. The riding position is sporting, rather than sit up and beg. Despite this, weight on the wrists is fairly low and two hours in the saddle presents no problems. The fairing offers reasonable protection, with the wind hitting the rider at about neck level. However the light weight of the bike coupled with the fairing does make the SRX a little vulnerable to being blown around by cross winds at highway speeds.

Carrying a pillion is do-able, but slows the bike down noticeably. However the pillion is faced with a very hard seat and poor grab handles. The bike has limited luggage carrying capacity in standard form.

Handling and braking are strong features of the SRX. The single cylinder design makes for very generous ground clearance, and the suspension was generally pretty well thought out. Steering is quick and light, and was not prone to shaking its head despite the 16 inch front wheel. Coupled with a torquey engine, the bike thrives in twisty conditions where handling and braking are more important than sheer power. Its light weight means riders do not tire trying to make the bike change direction quickly. It is quite simply great fun in tight conditions.

Fuel economy will never fall below 20km / litre, and 30km/ litre is achievable if you are careful when touring. Touring range thus works out at a very safe 230 to 250 km per tank.

In the workshop

As is typical for single cylinder bikes, the SRX is relatively cheap to run. There is not a lot for an owner to do, and what there is, is relatively easy. Transistorised ignition means no points to worry about. As with all small singles, frequent oil changes greatly lengthens the service life of the engine. My own example with oil changes every 1500km, was re-ringed for the first time at 56,000 km. It has now done about 70,000 km, and really needs a re-bore to restore performance

The bike comes from an era when manufacturers seemed to built bikes that were more home mechanic friendly. The oil filter is washable and re-useable, the air filter is oiled foam, the swingarm pivot shaft has grease nipples and the front forks have proper drain plugs at the bottom. Access to the spark plug is easy. The centrestand makes adjusting the drive chain and generally working on the bike, easy. Given all SRXs are now 18 odd years old, I'd fit a car style in-line fuel filter as soon as you can, and regularly dose the petrol tank with metho. This will vastly reduce the amount of carb hassles you will encounter.

A fairly complete service will take you about 2 hours or so to do, not including doing the valve clearances. The adjustment here is taken care of by shims. The manual suggests that clearances be checked every 6000km.

Being a single cylinder, the vibration does tend to get to the fasteners and loosen them off a bit. A routine part of your service will be going over the bike and checking the tightness of all the fasteners. The mounting screws on the fairing, plus the cylinder head and engine mounting bolts all seem to slacken off noticeably.

Due to its light weight and modest power, tyres tend to die of old age rather than wear. The standard front tyre size of 90/90/16 is hard to find, but going to a more common wider size sees the steering lose much of its precision. I ran oversize Dunlop GT301s on the front and found them disappointing. Going back to the stock size Michelin A39 made a huge improvement. Given regular oiling drive chains and sprockets also last for ages. With a little regular maintenance, 30,000km is obtainable out of a chain.

Cam chains seem to last quite well in SRXs. The chain can be replaced relatively easily when the valve clearances are being checked. My own SRX had the original cam chain replaced after 64,000km.

The electrics on the SRX have no particular weaknesses. Another nice touch on the SRX is the use of a resettable circuit breaker, instead of fuses.

Modifications

The front forks were always regarded as being a little soft. Replacing the standard 10 weight oil with 20 weight helps, as does putting in 15 millimetre of spacers on top of the springs.

Although in theory it is possible to fit the barrel off a XT/TT350 to the SRX, in practice its more trouble than its worth. The stock carby - which is really 2 carbies sharing a common float bowl - can be a bit frustrating to set up properly, especially if non standard exhausts are involved. It's a weirdo design with a very limited range of alternative jets and needles being available only from your friendly Yamaha dealer. I know of someone who have replaced the stock carbies with ones off a Kawasaki GPX250, although personally I remain unconvinced about whether this is really necessary.

High compression pistons for XT250s - which fit straight in - are available from White Bros, and alternative camshafts are produced by Megacycle.

To sum up The SRX was very popular with new riders and this tends to show when it comes to buying one now. Virtually all will have been through many owners, and some of those owners will have had no idea on how to maintain a bike. Having said that I have seen some really good low kilometre examples about. If you take your time, you will be rewarded with a small bike with genuine all-round ability. It has the character of a "single", can tour and is great around town or in the twisty bits. Despite having now bought a much bigger bike, I have no intention of ever selling my SRX. By: Cliff Alvey http://www.arcom.com.au/~Millal 11/28/02